The present invention relates to liquid crystal compositions for display devices and, more particularly, to a novel method for improving the decay time of a twisted nematic liquid crystal composition for use therein.
Display devices utilizing liquid crystal compositions of the nematic type are known to have relatively slow response speed, typically of the order of milliseconds, as compared to other display devices, such as light emitting diodes and the like, which respond in microseconds. It is known that the rise and decay times for a liquid crystal composition can be controlled electrically, by adjustment of the magnitude of the voltage applied to form a field switching the liquid crystal composition between its transmissive and absorptive states. Liquid crystal display devices desirably have low power requirements; in applications, such as watch displays and the like, wherein limited power is available, the circuitry driving the display device between its transmissive and absorptive states is typically simplified to even further minimize power drain by relying upon the spontaneous relaxation of the liquid crystal composition for the return of that composition to the unactivated state. Thus, the rise time to the desired light-transmissivity state is typically controlled by the magnitude of the applied driving voltage, while the decay time depends solely upon the spontaneous relaxation time of the liquid crystal composition itself.
A method is desirable for improving the decay time of twisted nematic liquid crystal compositions utilized in a display device, whereby the simplified drive circuitry (driving the display device for rise time transitions only) is retained.